Premature infants are prone to develop apneic spells, often associated with bradycardia, cyanosis, and acidosis. Although these spells often terminate spontaneously, resuscitation is frequently needed. The lack of response to these spells suggest that respiratory chemosensitivity in these infants may be abnormal. Since respiratory chemosensitivity is diminished during sleep in adults, the purpose of this project is to: (1) determine if respiratory chemosensitivity during sleep is decreased in premature infants, (2) if respiratory chemosensitivity during sleep is related to maturity of infants, and (3) if apnea of prematurity is a human model of the "crib death" (SIDS) syndrome. State will be determined by observation of the infants' activities and EEG recordings. CO2 sensitivity will be determined by the steady state method.